produce synthesis gas (Chap 7) that can be used to synthesize a wide variety of fuels and chemicals In addition to processing municipal waste, the technology can be used to create ethanol out of agricultural biomass waste, providing a potentially less expensive way to make ethanol than current corn-based plants The new system makes synthesis gas in two stages In the first stage, waste is heated in a 1200 C chamber into which a controlled amount of oxygen is added to partially oxidize carbon and free hydrogen Not all of the organic material is converted and some forms char which is then gasified when researchers pass it through arcs of plasma The remaining inorganic materials, including toxic substances, are oxidized and incorporated into a pool of molten glass which hardens into a material that can be used for building roads or discarded as a safe material in landfills The second stage is a catalyst-based process for converting synthesis gas into equal ethanol and methanol CO + 2H2 CH3OH CO + 3H2 C2H5OH 1154 Other Alcohols It is fairly common knowledge that the alcohols can be made from organic materials by fermentation There is, however, a potential for the production of alcohols from organic waste Historically, the production of methanol, ethanol, and higher molecular alcohols from syngas has been known since the beginning of the last century There are several processes that can be used to make mixed alcohols from synthesis gas including isosynthesis, variants of Fischer-Tropsch synthesis, oxosynthesis involving the hydroformylation of olefins, and homologation of methanol and lower molecular weight alcohols to make higher alcohols However, in the context of the Fischer-Tropsch process, depending on the process and its operating conditions, the most abundant products are usually methanol and carbon dioxide but methanol can be recycled to produce higher molecular weight alcohols With the development of various gas-to-liquids processes (Chaps 2 and 7) it was recognized that higher alcohols were by-products of these processes when catalysts or conditions were not optimized Modified Fischer -Tropsch (or methanol synthesis) catalysts can be promoted with alkali metals to shift the products toward higher alcohols Synthesis of higher molecular weight alcohols is optimal at higher temperatures and lower space velocities compared to methanol synthesis and with a ration of hydrogen/carbon monoxide ratio of approximately 1 rather than 2 or greater The first step in the synthesis to ethanol and higher alcohols is the formation of a carboncarbon bond Linear alcohols are then produced in stepwise fashion: nCO + 2nH2 CnH(2n + 1)OH + (n 1)H2O Stoichiometry suggests that the carbon monoxide/hydrogen ratio is optimum at 2, but the simultaneous presence of water-gas shift leads to an optimum ratio closer to 1 As in other synthesis gas conversion processes, the synthesis of higher molecular weight alcohols generates significant heat and an important aspect is choice of the proper reactor to maintain even temperature control which then maintains catalyst activity and selectivity In fact the synthesis of higher molecular weight alcohols is carried out in reactors similar to those used in methanol and Fischer-Tropsch synthesis These include shell and tube reactors with shell-side cooling, trickle bed, and slurry bed reactors Catalysts for the synthesis of higher molecular weight alcohols generally fall mainly into four groups: (a) modified high pressure methanol synthesis catalysts, such as alkali-doped ZnO/Cr2O3, (b) modified low pressure methanol catalysts, such as alkali-doped Cu/ZnO

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and Cu/ZnO/Al2O3, (c) modified Fischer-Tropsch catalysts, such as alkali-doped CuO/ CoO/Al2O3, and (d) alkali-doped sulfides, such as mainly molybdenum sulfide (MoS2) In the process, the feedstock enters the process (Fig 112) and is converted to synthesis gas (Chap 7) with the desired carbon monoxide/hydrogen ratio which is then reacted, in the presence of a catalyst, into methanol (CH3OH), ethanol (CH3CH2OH), and higher molecular weight alcohols CO + 2H2 CH3OH CO + 3H2 C2H5OH